Reinforced plastic material

ABSTRACT

A flexible, reinforced laminated plastic sheet material made from two sheets of multilayer thermoplastic material having a web of reinforcing strands received therebetween. The two sheets of material are bonded to each other in the interstices provided in the web. The contacting side of each sheet of material is composed of a layer of a thermoplastic having a lower melting point or sealing temperature than the outer layer of the multilayer thermoplastic material. The inner layers are bonded to each other without the use of any adhesive by passing the two sheets and the enclosed web between rotating heated laminating rolls.

United States Patent Inventors Appl. No. Filed Patented AssigneeREINFORCED PLASTIC MATERIAL 12 Claims, 11 Drawing Figs.

U.S.Cl 161/57, 156/177,156/179,156/309,156/324,16l/58,161/89,156/92,156/93,156/96,l56/140 lnt.C1 B32b 5/12, B32b 3l/04,C09i7/02 Field of Search 161/89,

92-96, 98,156, 252, 402, 57 59, 140, DIG. 2; 156/244, 306, 309, 310,324, 177, 179,178

Primary E.tanziner-William A, Powell Attorney-Donald L, JohnsonABSTRACT: A flexible, reinforced laminated plastic sheet material madefrom two sheets of multilayer thermoplastic material having a web ofreinforcing strands received therebetween. The two sheets of materialare bonded to each other in the interstices provided in the web. Thecontacting side of each sheet of material is composed ofa layer ofathermoplastic having a lower melting point or sealing temperature thanthe outer layer of the multilayer thermoplastic material. The innerlayers are bonded to each other without the use of any adhesive bypassing the two sheets and the enclosed web between rotating heatedlaminating rolls.

PATENTEDUCT 26 197i SHEET 10F 5 FIG. I.

SHEET 20F 5 'IIIII PATENTEBHU 26 1971 PATENTEnum 26 Ml SHEET 3 []F 5FIG. 6.

FIG. 7.

PATENTEU 25 3,616,130

Y SHEET u 0F 5 PATENTEuum 26 an 3,616,130

SHEET 5 UF 5 FIG. 9.

REINFORCED PLASTIC MATERIAL This application is a continuation-in-partof copending patent application Ser. No. 634,560, filed Apr. 28, I967,for .Reinforced Plastic Material," now abandoned.

BACKGROUND OF THE INVENTION 1. Field of theInvention This inventionrelates to a flexible, reinforced plastic sheet material and to a methodfor forming the material. More particularly the invention relates to alaminated plastic sheet material made from two sheets of a multilayerthermoplastic material having a web of strands received between the twoplastic sheets.

2. Description of the Prior Art Sheets of flexible, reinforced laminatedplastic material are finding increasing use in a wide variety ofapplications today. The advent of low-cost thermoplastic material, e.g.,polyethylene has increased the use of reinforced polyethylene as acovering for greenhouses, bams, temporary buildings, weatherproofinglarge buildings under construction, as a covering material for materialsstored in the open, e.g. lumber, grain, hay, and many other uses. Mostreinforced thermoplastic sheet material is manufactured by laminating aweb of strand material between two sheets of thermoplastic. Reinforcedfilm is commonly made by heat bonding thermoplastic film through theopenings provided in the web of reinforcing material, by applyingadhesive to the webor to one or more of the innerfaces of thethermoplastic material and pressing the plastic material to either sideof the reinforcing material, and by extruding one or more layers ofthermoplastic material onto a reinforcing material to provide a unitaryreinforced thermoplastic sheet. Among patents disclosing reinforcedthermoplastic material and methods for their manufacture are U.S. Pat.Nos. 2,851,389; 3,2l4,320; and 3,222,237.

The reinforcing material may be in the form of a prewoven scrim or wovenmesh material having wide openings between the strands. The strands fromwhich the web is prepared may be from either monofilament ormultifilament materials. In some cases it is preferred to lay auniformly arranged array of strands of reinforcing material into a webon one of the plastic sheets immediately prior to applying adhesivethereto or fusing the sheets together by heat. Machines for laying downa nonwoven scrim to provide reinforcement between sheets of plasticmaterial are shown .in US. Pat. Nos. 3,272,679; 3,l56,027;and 1,914,801.

SUMMARY OF THE INVENTION It is an object of this invention to provide areinforced laminated plastic sheet material having high bond strengthbetween the laminated plastic sheets.

It is a further object of this invention to provide a reinforcedlaminated plastic sheet material which does not require the use ofseparately applied adhesive materials.

It is also an object of this invention to provide a reinforced laminatedplastic sheet material which can be fabricated without subjecting theplastic laminae to heat damage.

It is a still further object of this invention to provide a reinforcedlaminated plastic sheet material which can be bonded by applying heat ata temperature below that normally used to heat laminate conventionalthermoplastic. It is another object of this invention to provide aneconomical process for manufacturing a reinforced laminated plasticsheet material.

The foregoing objects are realized in a flexible reinforced laminatedplastic sheet material having a first laminae of a preformed unitaryplastic sheet material having at least one outer layer of a firstflexible thermoplastic composition and an inner layer of a secondflexible thermoplastic composition having a melting point or sealingtemperature substantially below the first composition. A web composed ofuniformly arranged strands is applied to the inner layer of the firstlaminae of plastic sheet material. A second laminae having the samestructure as the first laminaehas its inner layer applied to the web andbonded to the first laminae in the interstices provided in the web.

By utilizing two sheets of thermoplastic material wherein each sheet iscomposed of at least two layers of thermoplastic material, one having alower sealing temperature than the other, it is possible to fabricatethe laminated plastic sheet material by the application of relativelylow pressures and low temperatures thereby avoiding damage to theheat-sensitive thermoplastic sheeting. Additional advantages areprovided in that the use of multilayer thermoplastic film avoids thenecessity of applying liquid or semiliquid adhesives to the web or tothe sheet material. It also avoids use of a molten polymer to form oneor more of the sheets of plastic material used to form the laminate.Further advantages are found in the laminate of the present invention inthat extremely high bond strengths are achieved by the use of relativelylow temperature and pressure.

BRIEF DESCRIPTION OF Til-IE DRAWINGS FIG. l is a schematic elevationalperspective view of one type of apparatus that may be utilized informing the reinforced laminate plastic material of the presentinvention;

FIG. 2 is a plan view, with sections. broken away, of a reinforcedlaminated plastic material prepared according to the present invention;

FIG. 3 is an enlarged CIOSSSCCIIOIIIHI view of FIG. 2 along the lines3.-3;

FIG. 4 is a further enlarged perspective broken view of a section of thelaminate shown in FIG. 3;

FIG. '5 is an enlarged perspective view of a portion of the laminate ofFIG. 3 rotated with portions broken away;

FIG. 6 is an elevational perspective view of another embodiment of thelaminate of the present invention, with portions broken away;

FIG. 7 is an elevational perspective view of still another embodiment ofthe laminate of the present invention, with portions broken away;

FIG. 8 is an elevational perspective view of still another embodimentofthe laminate of the present invention, with portions broken away;

FIG. 9 is a view similar to FIG. 3 wherein the laminate is made up ofsheets of plastic material each having three layers;

FIG. 10 is a further enlarged perspective view ofa section of thelaminate shown in FIG. 9; and

FIG. 111 is an enlarged perspective view of a portion of the laminate ofFIG. 9 rotated 90, with portions broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I thereinforced laminated plastic sheet material is designated generally bythe numeral 15. The laminate is formed from an upper sheet or laminae ofplastic material I7. These sheets are bonded together with a reinforcingnetwork of uniformly arranged strands of reinforcing material 18received between the two sheets of plastic material. As seen in FIGS. 2,3, and il, the reinforcing web I8 provides rectangular interstices, oropen spaces 19 between adjacent strands 20 of material. The plasticsheet material utilized to form the laminate is shown in FIGS. 3-3 ashaving two discrete layers of different thermoplastic material stronglybonded together. However it is understood that each plastic sheet mayhave any number of layers made of different thermoplastic material, e.g.three layers as shown in FIGS. 941. As seen in FIGS. 3 and t the upperplastic sheet or laminae I6 is composed of an outer layer of a firstthermoplastic material 16a and an inner layer of a second or differentthermoplastic material 16b. The lower sheet or laminae of plasticmaterial 117 is likewise composed of two discrete layers of differentthermoplastic material, the outer layer being designated 117a and theinner layer 17b. The thermoplastic sheet utilized in forming thereinforced laminate is preferably one commonly referred to as a duplex"film. The film can be conveniently made by coaxially extruding twodifferent thermoplastic materials from a single annular extruder die toform the film by the blown tube method. A method and apparatus forextruding multilayer film is disclosed in U.S. Pat. 3,223,761. the

disclosure of which is hereby incorporated by reference. Films preparedaccording to the process and apparatus of the foregoing patent have twoor more discrete layers which are so strongly bonded together that thelayers cannot be peeled apart.

The multilayer film used in fabricating the embodiment of the laminateof the present invention shown in FIGS. 1-9 has an inner layer ofthermoplastic material 16b and 17b that is made from a thermoplasticmaterial which has a lower melting point or sealing temperature thandoes the thermoplastic material used for the outer layer 16a or 17a. Oneof the preferred films for manufacturing the laminate of the presentinvention is a duplex sheet wherein the outer layer thermoplasticmaterial is low-density polyethylene and the inner layer ofthermoplastic material comprises a copolymer of ethylene and vinylacetate. It is important that the thermoplastic material used for theinner wall or layer have a melting point or sealing temperature which isat least 5 F. below the melting point or sealing temperature of thethermoplastic material from which the other layer or layers of thethermoplastic sheet material is made. It is preferred to have an innerlayer of a thermoplastic material which has a sealing temperature about30 F. lower than that of the other layer or layers of thennoplasticmaterial. A particularly advantageous combination in a dual wall filmwhich provides the difference in softening points is low-densitypolyethylene as the outer layer and ethylene-vinyl acetate copolymer asthe inner layer. The lowdensity polyethylene used for the outer layermay have a melting point of from about 140 F. to about 225 F. and theethylene-vinyl acetate copolymer will have a melting point of from about110 F. to about 170 F. The melting point of the ethylene-vinyl acetatecopolymer varies substantially with the vinyl acetate content of thecopolymer. Ethylenevinyl acetate copolymers found particularly suitablefor use in the present invention are those containing from about 1percent by weight vinyl acetate up to about 30 percent vinyl acetate inthe copolymer. Preferably the copolymer contains from about to'25percent vinyl acetate. A more particularly preferred vinyl acetatecontent is from about to weight percent. Inner layers made from 15 to 20percent vinyl acetate copolymer exhibit very good adhesive propertieswhen modest pressures and relatively low laminating temperatures areused. One particular low-density polyethylene which has been foundeminently suitable for making the outer layer of the thermoplastic sheetmaterial used in preparing the laminate of the present invention isDFDU-4400 to which is added about 4 percent of 0836 low-densitypolyethylene resin. The melt temperature of the DFDU-4400 resin isapproximately 235 F. and the melt temperature of the 0836 resin isapproximately 235 F. Each of the foregoing resins are manufactured byUnion Carbide Corporation. The ethylene-vinyl acetate copolymerespecially preferred for use in the inner layer is the ethylene-vinylacetate copolymer designated DQDG-l868 manufactured by Union CarbideCorporation. This copolymer contains 18-20 percent weight vinyl acetatein the copolymer.

Another group of copolymers which are eminently suitable for preparingthe inner layer of the multilayer film utilized in the laminate of thepresent invention are copolymers of ethylene with acrylic acid,methacrylic acid, esters of acrylic acid, and esters of methacrylicacid. Examples of suitable acrylic esters for polymerization withethylene are all acrylate, methyl acrylate ethyl acrylate, butylacrylate and octyl acrylate. Examples of suitable methacrylate estersare methyl methacrylate, ethyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, cyclohexyl methacrylate, allyl methacrylate andlauryl methacrylate. In general the percentage of the comonomer to becopolymerized with ethylene should range from about 1 percent to up toabout percent. The most satisfactory films for use as the inner layer ofthe laminate are obtained when the ethylene content of the acrylic acidof methacrylic acid or one of their esters copolymer is from 15 to 25percent weight. Smaller quantities of the comonomers should be used whenthe long chain alcohol esters are utilized as comonomers, e.g., as whenusing the lauryl methacrylate ester as the comonomer.

The invention is not limited to the use of ethylene-vinyl acetate orethylene-acrylic acid or methacrylic acid or their esters thereof as theinner layer film forming material in the multilayer films used in thelaminate of the present invention. Other film forming polymers andcopolymers are also suitable for forming the inner layer of themultilayer film. The primary criteria to be kept in mind is that themelting point or the sealing temperature of the polymer used for theinner layers be at least 5 below that of the polymer used to form theother film layer or layers in the multilayer film. The sealingtemperature is defined as the temperature at which two pieces of thethermoplastic will bond together under moderate pressure.

While polyethylene has been described as a preferred material forforming the outer layer of a duplex thermoplastic sheet material thatmay be used for making the laminate, the invention is not limited to theuse of this polymeric material. Any thermoplastic material which can beextruded in conjunction with a lower melting thermoplastic material andwhich has a compatibility sufficient to form a multilayer film having ahigh bonding efficiency is suitable for use in fonning the outer layeror layers of the multilayer film. Among those plastic materials whichcan be used to form the outer layer or layers of the plastic sheet forpreparing the laminate of the present invention are nylon, copolymers ofethylene with other comonomers, high-density polyethylene,polypropylene, propylene copolymerized with other comonomers,polycarbonate, polyvinyl chloride, vinyl chloride, or vinyliden chloridecopolymers, polyvinylidene chloride, polyvinyl alcohol, polyesters,polystyrene, polybutyrates, and many other thermoplastic materials whichcan readily be extruded to make flexible film using the coaxialextrusion process described in the aforementioned patent.

The web of reinforcing material 18 may be made of woven or nonwovenstrands arranged in an open mesh network. The strands may be composedofa monofilament material or multifilament material. One can use naturalor synthetic material to form the individual strands or threads frommultifilament stock. Strands may be monofilament synthetic materials ormultifilament synthetic materials such as viscose rayon, acetate rayon,polypropylene, polyvinyl chloride, polyvinylidene chloride, copolymersof vinyl chloride or vinylidene chloride, nylons, cellulose butyrate,polystyrene, polyester, polyvinyl alcohol, and other commerciallyavailable organic filament material. Naturally occurring inorganicmaterials may be used to form the strands, either of mono ormultifilament. Examples of inorganic material which have been foundsuitable for forming the strands are metals, glass, and asbestos.

Naturally occuring organic materials that can be spun into strands canbe used to make the reinforcement material. Among those that have beenfound suitable are cotton, wool, hemp, and twisted paper for making thestrands.

A preferred material for forming a web of reinforcing material is rayon,preferably multifilament strands. This material furnishes adequatestrength and is economical. However, if increased strength is requiredin the reinforced material nylon multifilament strands are verysatisfactory. Also high strength can be gained from the use ofmonofilament and multifilament glass fibers either woven or nonwoven.

Twisted and untwisted multifilamentary materials are equally suitablefor use in manufacturing the web of reinforcing material 18. Whentwisting is desired it may range from one-half turn per foot to 20 turnsor more per inch. The denier of the strand material can vary over a widerange, from about 200 to about 2,500 denier strands have been foundsuitable. As shown in laminated plastic material depicted in F 168. 2-5the warp or longitudinal thread of the web 18 utilize two strands 20-20having a slight twist and being looped over the single fill ortransverse strand 21 the web 18. Each of the strands 20-are made ofmultifilament fibers, for example hightenacity rayon.

Referring to FIG. 6, there is shown an embodiment of the laminate of thepresent invention which is readily manufactured using a monofilamentsynthetic strand 22 for both the warp and fill strands in the laminatematerial. in this construction the warp and fill threads are nonwovenand may be readily formed into a regular patternby laying the strands22-22 in a rectangular pattern using a scrim laying apparatus such asthat described in aforementioned U.S. Pat. Nos. 3,272,679; 3,156,027; or1,914,801. The laminate depicted in HQ. 7 the reinforcing web 18 is madefrom a prewoven scrim utilizing multifilamentary strands 23 for both thewarp and fill threads. Each fill thread is passed through the middle ofthe warp thread in a transverse direction, as seen at numeral 24,providing a woven scrim. As seen in FIG. 8 the filamentary web 18 may bemade from an integrally formed, prewoven mesh material composed ofmonofilament synthetic strands 25. This type web is advantageouslyformed from synthetic thermoplastic materials such as nylon orpolyester-type materials and fabricated by extruding an integrallyformed net of material. The warp and fill threads are fused together attheir intersection, as shown at numeral 26.

Referring now to FIG. 1, the laminated plastic material of the presentinvention may be made by the laminating apparatus designated generallyby the numeral 27. The web of preformed reinforcing material 18 iswithdrawn from a supply .roll 28 of scrim-type web material. The web isfed between the nip of two laminating rollers 29-29. One or both of thelaminating rollers are supplied with heat in the form of electricalheaters or steam or any other suitable source of heat (not shown). Theupper multilayer sheet of the plastic material 16 is fed into the nip ofthe rollers 29-29 with its inner layer facing and contacting the web ofreinforcing material 18. The upper sheet of material 16 is convenientlysupplied to the laminator by rolls withdrawing from storage roll 30.Since the inner layer of thermoplastic material 161; on the multilayerfilm could become somewhat tacky under certain storage conditions andthis may result in distortion of the film when unrolled at high speeds,it is advisable to provide a separate drive assembly to draw the filmfrom the roll 30 to prevent undue elongation and distortion of the film16. In the apparatus depicted supply rollers 31 and 32 are utilized todraw the film from the storage roll 30 and supply it to the nip of thepressure rollers 29-29. The driven upper supply roller 31 may beconveniently powered by an electrical motor or other suitable powerdevice designated 33. The lower supply roller 32 can be optionallydriven if desired. After leaving the nip of the pair of drive rolls31-32 the upper sheet of thermoplastic material 16 may optionally bepassed over an upper preheat roller 34. This roller is supplied with asource of heat and is maintained at a temperature somewhat lower thanthe temperature of the laminating rolls 29-29. The preheat rollincreases the production rate of the laminate by preheating the innerlayer of thermoplastic material 16b to soften it and cause it to adhereto the inner layer 17b of the sheet 17 without requiring the laminatingrollers 29-29 to be operated at a high temperature.

The lower sheet of thermoplastic material 17 is drawn from storage roll35 by means of a set oflower supply rollers 36-37. A drive unit 38similar to the upper drive unit is provided to actuate the lower supplyrollers 36-37.

A wide range of temperatures may be utilized to laminate the upper andlower sheet of thermoplastic material together in the interstices of theweb material. When a polyethylene material is utilized for the upper andlower laminae and an ethylene-vinyl acetate copolymer is utilized forthe inner layer of each sheet of thermoplastic material, it has beenfound that a surface temperature range of from about 150 F. to about 450F. on either or both of the laminating rollers 29 is satisfactory. Atemperature in this range will produce a good bond between the upper andlower sheets 16 and 17. it should be noted that the temperatures atwhich the laminating roll or rollers are operatedwill be dependent upon(1) the ethylene content of the thermoplastic material utilized for rheinner layer of each sheet of plastic material, (2) the surface speed atwhich the laminating rollers are operated. When ethylenevinyl acetatecopolymer is used the temperature necessary for lamination will decreaseas the vinyl acetate contend of the copolymer increases. It will also beappreciated that the bonding temperature will be dependent to someextent upon the pressure exerted in the nip of the llaminator rolls.With increased pressure lower temperatures may be utilized to effect thebond between the sheets 16 and I7, however, the pressure which can beapplied by the laminating rolls is limited to a pressure that will notcause damage by puncturing or thinning of the outer layers ofthermoplastic material 16a and 17a in the areas where the warp and fillthreads of the web 18 cross each other. The preferred laminating rolltemperature when using low density polyethylene and an ethylene-vinylacetate copolymer for the inner layer containing about 15 to 25 percentvinyl acetate will range from about l75 F. to about 250 F. for each ofthe laminating rollers 29-at web speeds of from about to about 200 feetper minute.

The laminating rollers 29-29 may be made from steel or any othersuitable heat conducting material. It is preferred that at least one ofthe laminating rollers be covered by a material which has a degree ofresiliency which will prevent the cutting or thinning of thethermoplastic film by pressure appliedto the laminate from the rollers.lln one exemplary apparatus construction similar to that depicted in H6.1 each of the laminating rolls 29 were covered with a nonmetallicmaterialwhich provided some degree of resiliency. The upper roll, madeof steel, was covered with a thin coat of Teflon, and the lower roll wascovered with a silicone rubber sleeve. This arrangement provided goodheat transfer and yet did not use a thinning or cutting of the upper orlower thermoplastic sheet material in the area where the warp and fillthreads crossed. When utilizing the upper preheat roller 34 and lowerpreheat roller 39 in the aforementioned apparatus it was found thatthese rollers produced a good bond and a high production rate for thelaminate when they were operated at about F. It should be understoodthat the temperature of both the laminating rollers 29-29 and thepreheat rollers 3439 will have to be adjusted depending upon theparticular polymeric material used for the inner layer thermoplasticmaterial in the multilayer sheets 16 and l? and will also be dependentupon the thickness of the thermoplastic multilayer sheets 16 and 17.Thicker sheets will necessarily require a high operating temperature forthe laminating rollers and the preheat rollers.

It is realized that other laminating apparatuses may be used toconveniently carry out the process aspects of the present invention. Asetated hereinbefore the web of reinforcing material 18 may be formed inplace utilizing machines similar to that d epictedin the patentsmentioned hereinbefore. Additionally the upper and lower sheets ofduplex film 116 and 17 may be formed at the location of the laminatorand fed directly to the pressure rolls 29-29 while still in asemiformative warm condition. Instead of utilizing upper and lowerpreheat rollers 34 and 39, one may conveniently utilize a bank or row ofelectrical heating lamps in the position occupied by the preheat rollersto soften the inner layer of the upper and lower sheet material 16 and17.

in one embodiment of the present invention a laminated plastic materialwas made utilizing a multilayer film having two layers wherein the outerlayer of thermoplastic material was formed from a mixture of two gradesof low density polyethylene. The outer layer was made from 9BpercentUnion Carbide polyethylene designated DFDU-4,400 and 2 percent of UnionCarbide polyethylene designated 0836. The inner layer of thermoplasticmaterial was an ethylene-vinyl acetate commercially available materialfrom Union Carbide DOUG-1868 which contained 18 percent vinyl acetate.The multilayer film was formed by the coaxial extrusion method disclosedin aforementioned U.S. Pat. 3,223,761. The multilayer film produced fromthe foregoing thermoplastic materials contained a low-densitypolyethylene outer layer which was appreximately 1% miL-thiclt and hadan inner layer of the ethylene-vinyl acetate copolymer which was 16mil.- thick. The laminate was made by utilizing an apparatus having apair of heated laminating rolls, one being maintained at 175 F. and theother at 200 F. Preheat was supplied to each of the utilizing prior artmethods, i.e., heat laminating two sheets of thermoplastic materialtogether over a reinforcing scrim. The peel strengths of the laminate ofthe present invention are so high that they cannot be measured, i.e.,the laminated film sheets of thermoplastic material by means of a row ofelectritears before it will peel between the bonded layers. By utilizingcal heaters arranged ahead of the nip of the laminating rolls. amultilayer film to form the reinforced plastic material of the Thereinforcing web 18 was made from multifilament rayon present invention,degradation of the thermoplastic outer prewoven strand material using aleno weave similar to that layers of the laminate are prevented. One isable to utilize depicted in the web 18 shown in FIG. 5. The warp threadwas much lower temperatures for bonding the sheets of thercomposed oftwoseparate strands of 550 denier multifilament l0 moplastic to each otherwhen using the multilayer films to rayon thread. The fill thread was a1,100 denier multifilament make the laminates of this invention. This isparticularly imtwisted strand. The warp threads were slightly twistedand also portant when working with films which are readily damaged hadone turn looped in between each of the fill threads. The by excessiveheat, e.g., polyvinyl chloride sheeting. spacing between the warp andfill threads provides an opening roughly /a-inch square. An excellentbond was achieved at the As pointed out hereinbefore the multilayer filmSheets used innerface of inner layers of ethylene-vinyl acetate portionof to fabricate the laminated reinforced material y have 3 P the filmused to make the laminate. With this particular conof different layersof thel'l'noplami material in each struction and temperature used forlamination very little Sheet- In the embodiment shown FIGS the "PP"direct adhesion is obtained between the inner ply of ethylene- Shae ofPlastic material 40 y have an Outer layer Ofone i l acetatethermoplastic d h woven scrim 13 If i i plastic material. anintermediate layer 40b of another plastic desired to provide directadhesion of h filament on strands material, and an inner layer 400 ofstill another plastic materiof the web to the upper and lower sh of l ii l al. The lower sheet of plastic material 41 likewise has an outerthis may conveniently be accomplished by using a higher k layer 41a ofone plastic material, an intermediate layer 41b of (lower melting point)thermoplastic for the inner layer f another plastic material, and aninner layer 41c ofstill another sheets 16 and 17. However, even withoutadhesion of the plastic material. The same reinforcing material 18having threads directly to the inner and outer layers excellent warpthreads 20 and fill threads 21 as described hereinbefore strength isobtained by virtue of the high bond obtained may be used to reinforcethe two plastic sheets 40 and 41. Any between th nta i g interfa f h i ela e 16!; d combination of different plastic materials may be used toform 17b. The laminate manufactured according to the foregoing themultiple layer films such as ethylene-vinyl acetate procedure wascompared in tests with other laminates using copolymer for the innerlayer polypropylene for the interdifferent web materials alsomanufactured in accordance with mediate layer, and lOW densitypolyethylene for the outer the present invention. An additional sampleof commercially layer. If desired the outer layer may be a plasticcontaining a available reinforced laminate made from polyethylene and acolor or a filler such as carbon black, titanium dioxide, or aluprewovenscrim by heat fusing the single layers of minum powder. Also the outerlayer of each sheet of plastic polyethylene layers together was obtainedand tested for commay be covered by a metal foil such as aluminum whenit is parison. The results of the test appear below. desired.

Reinforcing web intermediate Failure ------V- ,vi yield LaminateManulacstrength, strength, Test sample film turer Material Weave Denieris 1 p.s.i.

l 1 Nylon Layed 400 32 53 g n i t gii Li-T13 's-sto 35 4 stair l i n1-1100} 37 43 5 Y jf fig 14 3.1

Multilayer film 1-% mil low density polyethylene outer layer and y milethylene-vinyl acetate inner layer.

2 Commercial prior art laminate made using two shetts of low densitypolyethylene each 2.0 mil thick bonded by heat between openings inreinforcing web.

it 4 i The above tests were conducted on 6-inch square swatches oflaminate. Each of the samples, except sample 5, were prepared by heatingfor 5 to 10 seconds at a pressure of 100-150 pounds at 250 F. the weband the thermoplastic materials between one unyielding platen and oneresilient platen in a hydraulic press. The tear test reported above wasan arbitrary test made on an Instron tensile tester. One corner of eachof the 6-inch square swatches of laminated material was gripped by theupper jaws of the tester and a wire hook with xii-inch radius turn wasinserted into each sample of laminate at a point 4 inches above thelower corner. The hook was attached to the lower jaws of the tester. Thelnstron jaws were moved apart at a rate of 2.0 inches per minute. Thesamples were tested at ambient temperature, i.e., about 76 F. Theintermediate yield strength reported above is the p.s.i. gauge readingon the Instron tester at which the first tear began to form in thelaminated material. The failure yield strength in p.s.i. reported aboveis the gauge reading on the lnstron tester when the hook pulled out orthrough the laminated material.

It will be seen from the above that the laminated material of thepresent invention is substantially stronger than that made The foregoingdisclosure and description of the invention is illustrative andexplanatory thereof and, in light thereof, other modifications will beapparent to those skilled in the art. Therefore, the present inventionis to be limited only by the scope of the appended claims.

What is claimed is:

1. A flexible, reinforced, laminated plastic sheet material consistingof:

a. a first lamina of a preformed unitary sheet of plastic materialhaving an outer layer of a first flexible, thermoplastic composition andan inner layer of a second flexible, thermoplastic composition selectedfrom the group consisting of ethylene-vinyl acetate copolymers,copolymers of ethylene with acrylic acid, methacrylic acid, esters ofacrylic acid, and esters of methacrylic acid, said second compositionhaving a sealing temperature of about 30 F. lower than that of saidfirst composition;

. a web composed of strands applied to said inner layer of said firstlamina of plastic sheet material; and

c. a second lamina having the same structure as the first lamina havingits inner layer applied to said web and bonded to said first lamina inthe interstices provided in said web.

2. The article defined in claim 1 wherein said outer layer is aboutthree times the thickness of said inner layer.

3. The article defined in claim 1 wherein said web is form ed from asingle multifilament fill thread and a pair of twisted multifilamentwarp threads, each of said warp threads passing over different sides ofsaid fill thread.

4. The article defined in claim 1 wherein said web comprises nonwovenmonofilament warp and fill strands laid in a rectangular pattern.

5. The article defined in claim 1 wherein said web comprises a prewovenscrim having multifilament warp and fill threads, each of said fillthreads being passed through said warp threads in a transversedirection.

6. The article defined in claim 1 wherein said inner layer consists of acopolymer of ethylene with acrylic acid.

7. The article defined in claim 1 wherein said inner layer comprises anethylene-vinyl acetate copolymer containing from about 1 percent up toabout 30 percent weight vinyl acetate.

8. The article defined in claim 7 wherein contains from about weight ofvinyl acetate.

9. The article defined in claim 7 wherein said outer layer comprisespolyethylene.

said copolymer percent up to about percent by 10. A flexible,reinforced, laminated plastic sheet material consisting of:

a. a first lamina of a preformed unitary sheet of plastic materialhaving a plurality of outer layers of different flexible thermoplasticcompositions and an inner layer of a flexible thermoplastic compositionselected from the group consisting of ethylene-vinyl acetate copolymers,copolymers of ethylene with acrylic acid, methacrylic acid, esters ofacrylic acid and esters of methacrylic acid, said second compositionhaving a sealing temperature of about 30 F. lower than that of any ofsaid outer layers;

b. A web composed of strands applied to said inner layer of said firstlamina of plastic sheet material; and

c. a second lamina having the same structure as the first lamina havingits inner layer applied to said web and bonded to said first lamina inthe interstices provided in said web.

from about 1 percent up to about 30 percent weight vinyl acetate.

12. The article defined in claim 1 wherein said plurality of outerlayers comprises at least one layer of polypropylene and one layer ofpolyethylene.

M050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.5,616,130 Dated October 26, 1971 Inventor(s) John E. Rogosch et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- The Abstract, line 2, reads of multilayer", should read of amultilayer Column 2, line 42, reads "perspective view", should readperspective broken View Column 2, line 51, reads "material 17.", shouldread material 16 and a lower sheet or laminae of plastic material 17.Column 5, line 63, reads "are all acrylate", should read are allylacrylate Column 5, line 64, reads "methyl acrylate ethyl acrylate",should read methyl acrylate, ethyl acrylate Column 4, line 10, reads"inner layers, should read inner layer Column A, line 31, reads "orvinyliden", should read or vinylidene Column 4, line 75, reads "strand21 the web, should read strand 21 of the web Column M, line 7%, reads"strands 20-are", should read strands 20-21 are Column 6,

line 18, reads rollers 29-at", should read rollers 29-29 at Column 6,line 32, reads "use a", should read cause a Column 6, line 66, reads"DFDU-4,#OO", should read DFDU-QQOO Column 7, line 22, reads "filamentson strands", should read filaments or strands Column 10, line ll, reads"30 F., should read 30F. Column 10, line 25, reads "Claim 1", shouldread Claim 10 Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. The article defined in claim 1 wherein said outer layer is aboutthree times the thickness of said inner layer.
 3. The article defined inclaim 1 wherein said web is formed from a single multifilament fillthread and a pair of twisted multifilament warp threads, each of saidwarp threads passing over different sides of said fill thread.
 4. Thearticle defined in claim 1 wherein said web comprises nonwovenmonofilament warp and fill strands laid in a rectangular pattern.
 5. Thearticle defined in claim 1 wherein said web comprises a prewoven scrimhaving multifilament warp and fill threads, each of said fill threadsbeing passed through said warp threads in a transverse direction.
 6. Thearticle defined in claim 1 wherein said inner layer consists of acopolymer of ethylene with acrylic acid.
 7. The article defined in claim1 wherein said inner layer comprises an ethylene-vinyl acetate copolymercontaining from about 1 percent up to about 30 percent weight vinylacetate.
 8. The article defined in claim 7 wherein said copolymercontains from about 15 percent up to about 20 percent by weight of vinylacetate.
 9. The article defined in claim 7 wherein said outer layercomprises polyethylene.
 10. A flexible, reinforced, laminated plasticsheet material consisting of: a. a first lamina of a preformed unitarysheet of plastic material having a plurality of outer laYers ofdifferent flexible thermoplastic compositions and an inner layer of aflexible thermoplastic composition selected from the group consisting ofethylene-vinyl acetate copolymers, copolymers of ethylene with acrylicacid, methacrylic acid, esters of acrylic acid and esters of methacrylicacid, said second composition having a sealing temperature of about 30F. lower than that of any of said outer layers; b. A web composed ofstrands applied to said inner layer of said first lamina of plasticsheet material; and c. a second lamina having the same structure as thefirst lamina having its inner layer applied to said web and bonded tosaid first lamina in the interstices provided in said web.
 11. Thearticle defined in claim 10 wherein said inner layer comprises anethylene-vinyl acetate copolymer containing from about 1 percent up toabout 30 percent weight vinyl acetate.
 12. The article defined in claim1 wherein said plurality of outer layers comprises at least one layer ofpolypropylene and one layer of polyethylene.